The present invention relates to a method and apparatus for converting particles of tobacco, fibrous tobacco smoke filtering substances or analogous fibrous materials into a continuous stream, and more particularly to improvements in a method and apparatus for forming a continuous rod-like filler of such fibrous material. A filler is a stream which has been relieved of surplus material and is ready to be draped into a web of cigarette paper or other wrapping material to form therewith a rod which can be subdivided into filter rod sections or plain cigarettes, cigarillos or cigars of unit length or multiple unit length.
A tobacco filler is formed in a so-called rod making machine wherein shreds or otherwise configurated particles of tobacco are showered into an elongated path to form a stream with an irregular (fluctuating) surplus of particulate material. The surplus is thereupon removed by a trimming or equalizing device, and the resulting filler is draped into a web of cigarette paper or the like with simultaneous compacting of the filler and bonding of overlapping marginal portions of the web to each other before the resulting rod passes through a suitable cutoff. The making of a continuous filter rod is analogous except that, if the particulate material consists of filaments which are made of a suitable synthetic plastic material and form a so-called tow which is sprayed with atomized plasticizer and thereupon passes through a gathering horn prior to draping into a web of cigarette paper, imitation cork or the like, the trimming operation can be omitted.
It is already known to monitor the density of the filler prior or subsequent to draping and to regulate one or more parameters which influence the density as a function of changes in the characteristics of signals which are generated by the density monitoring device.
German Auslegeschrift No. 11 59 326 discloses a cigarette rod making machine wherein the RPM of the distributor and the speed of the tobacco transporting conveyor (which receives particles of tobacco from the distributor) can be regulated in response to signals which denote the monitored density of the filler.
U.S. Pat. No. 3,731,693 discloses the possibility of regulating the pressure in a suction chamber adjacent to a tobacco transporting conveyor in response to signals which denote the density of the trimmed tobacco stream (filler).
U.S. Pat. No. 3,338,247 discloses a machine wherein the quantity of removed surplus tobacco is monitored downstream of the equalizing station and the thus obtained signals are used to regulate the operation of the distributor with a view to maintain the surplus at a constant value. None of the above proposals are entirely satisfactory because the density of the filler (and hence its resistance to the passage of smoke therethrough as well as the quantity of fibrous material therein) still tends to deviate from the optimum density.